单项选择题
A.low steel on the Huey P. Long Bridge
B.mean sea level
C.the local water table
D.the minimum dam control level
单项选择题 Most drill ships and barges have a walled opening below the derrick，open to the water’s surface and through which various drilling tools can pass down to the sea floor called a （）.
单项选择题 Most covered lifeboats will right themselves after capsizing if the（）.
单项选择题 Mean low water is the average height of（）.